"Glaucomas" are a group of debilitating eye diseases that are the leading cause of preventable blindness in the United States and other developed nations. Primary Open Angle Glaucoma ("POAG") is the most common form of glaucoma. The disease is characterized by the degeneration of the trabecular meshwork, leading to obstruction of the normal ability of aqueous humor to leave the eye without closure of the space (e.g., the "angle") between the iris and cornea (see, Vaughan, D. et al., In: General Ophthamology, Appleton & Lange, Norwalk, Conn., pp. 213-230 (1992)). A characteristic of such obstruction in this disease is an increased intraocular pressure ("IOP"), resulting in progressive visual loss and blindness if not treated appropriately and in a timely fashion.
The disease is estimated to affect between 0.4% and 3.3% of all adults over 40 years old (Leske, M. C. et al., Amer. J. Epidemiol. 113:1843-1846 (1986); Bengtsson, B., Br. J. Ophthamol. 73:483-487 (1989); Strong, N. P., Ophthal. Physiol. Opt. 13:3-7(1992)). Moreover, the prevalence of the disease rises with age to over 6% of those 75 years or older (Strong, N. P., Ophthal. Physiol. Opt. 12:3-7 (1992)).
A link between the IOP response of patients to glucocorticoids and the disease of POAG has long been suspected. While only 5% of the normal population shows a high IOP increase (16 mm Hg) to topical glucocorticoid testing, over 90% of patients with POAG show this response. In addition, an open angle glaucoma may be induced by exposure to glucocorticoids. This observation has suggested that an increased or abnormal glucocorticoid response in trabecular cells may be involved in POAG (Zhan, G. L. et al., Exper. Eye Res. 54:211-218 (1992); Yun, A. J. et al., Invest. Ophthamol. Vis. Sci. 30:2012-2022 (1989); Clark, A. F., Exper. Eye Res. 55:265 (1992); Klemetti, A., Acta Ophthamol. 68:29-33 (1990); Knepper, P. A., U.S. Pat. No. 4,617,299).
The ability of glucocorticoids to induce a glaucoma-like condition has led to efforts to identify genes or gene products that would be induced by the cells of the trabecular meshwork in response to glucocorticoids (Polansky, J. R. et al., In: Glaucoma Update IV, Springer-Verlag, Berlin, pp. 20-29 (1991)). Initial efforts using short-term exposure to dexamethasone revealed only changes in specific protein synthesis. Extended exposure to relatively high levels of dexamethasone was, however, found to induce the expression of related 66 kD and 55 kD proteins that could be visualized by gel electrophoresis (Polansky, J. R. et al., In: Glaucoma Update IV, Springer-Verlag, Berlin, pp.20-29 (1991)). The induction kinetics of these proteins as well as their dose response characteristics were similar to the kinetics those that were required for steroid-induced IOP elevation in human subjects (Polansky, J. R. et al., In: Glaucoma Update IV, Springer-Verlag, Berlin, pp. 20-29 (1991)). Problems of aggregation and apparent instability or loss of protein in the purification process were obstacles in obtaining a direct protein sequence.
Because increased IOP is a readily measurable characteristic of glaucoma, the diagnosis of the disease is largely screened for by measuring intraocular pressure (tonometry) (Strong, N. P., Ophthal. Physiol. Opt. 12:3-7 (1992 ), Greve, M. et al., Can. J. Ophthamol. 28:201-206 (1993)). Unfortunately, because glaucomatous and normal pressure ranges overlap, such methods are of limited value unless multiple readings are obtained (Hitchings, R. A., Br. J. Ophthamol. 77:326 (1993); Tuck, M. W. et al., Ophthal. Physiol. Opt. 13:227-232 (1993); Vaughan, D. et al., In: General Ophthamology, Appleton & Lange, Norwalk, Conn., pp. 213-230 (1992); Vernon, S. A., Eye 7:134-137 (1993)). For this reason, additional methods, such as direct examination of the optic disk and determination of the extent of a patient's visual field loss are often conducted to improve the accuracy of diagnosis (Greve, M. et al., Can. J. Ophthamol. 28:201-206 (1993)).
In view of the importance of glaucoma, and the at least partial inadequacies of prior methods of diagnosis, it would be desirable to have an improved, more accurate method for diagnosing glaucoma. The present invention provides such improved diagnostic agents and methods.